Hemodialysis is a blood treatment procedure for patients with renal failure or in other cases where the kidneys cannot adequately cleanse the blood of toxins. During hemodialysis, the patient's blood is withdrawn, filtered of toxins, and returned to the blood stream. The dialysis procedure takes several hours and is done several times a week. The long hours and the frequency of the dialysis treatment in patients with renal failure requires reliable, continued access to the venous system for blood exchange. Long-term venous access mechanisms commonly used for hemodialysis treatment include vascular access ports, dialysis grafts and hemodialysis catheters.
One type of blood treatment catheters well known in the art is a dual-lumen hemodialysis catheter. These catheters are designed to provide long-term access to the venous system for dialysis. In one form, the dialysis catheter contains two lumens, a withdrawal lumen for withdrawing blood to be treated from a blood vessel and a supply lumen for returning cleansed blood to the vessel. The distal segment of the catheter is preferably positioned at the junction of the superior vena cava and right atrium to obtain a blood flow of sufficient volume to accommodate dialysis treatment requirements.
Dual lumen, split tip hemodialysis catheters are dialysis catheters in which the two lumens include two separate proximal tube segments and two separate distal tube segments. These two separate distal tip tubes are known as split tips. Split tip catheters have several advantages over unitary multi-lumen catheters. Each of the distal tube segments is capable of moving independently of the other tube and can provide fluid flow around the entire circumference of the distal ends of the catheter tubes. This fluid flow pattern decreases the likelihood of catheter occlusion with the wall of the vessel. In addition, scientific studies have indicated that the split tip catheter design may reduce the amount of fibrin or other material build-up at the distal end of the catheter.
Although superior in performance to unitary dual-lumen dialysis catheters, the split tip catheter design makes the process of inserting the catheter into the patient more complex. There are two generally accepted techniques for inserting dual-lumen, split tip dialysis catheters. One technique is to use a dilator/sheath, while the other is a guide wire weaving method.
The dilator/sheath technique is more commonly used. In that technique, split tip catheters are placed through a split-able or tear-away sheath. After accessing the target vein with a needle and guide wire, the sheath/dilator is advanced over the guide wire into the vein. Once the puncture site is sufficiently expanded, the guide wire and dilator are removed leaving only the sheath in place. The distal tip of the split tip catheter is then manually inserted into the sheath and advanced into the vein. The physician inserts both tubes into the sheath. Once the catheter is in position within the vein, the sheath is slowly pulled out while the visible portion of the sheath is simultaneously split into two.
One major problem associated with the sheath/dilator technique of insertion is the increased chance of air embolism due to the large size and location of the insertion site. An air embolism occurs when air enters the venous system through an opening caused by the insertion of the dialysis catheter. The low-pressure gradient of the venous system combined with intake of breath by the patient can create a negative pressure in the area of the puncture site. Negative pressure causes the ambient air to flow through the puncture site and into the blood stream. If air bubbles in the blood stream reach a sufficient volume, they can interfere with the normal pumping of blood by the heart, with fatal consequences.
To ensure against a possible air embolism, the physician should occlude the sheath immediately after the dilator is removed. The vein may also be exposed to air during the time required to insert the catheter into the sheath. The sheath insertion technique is further complicated by the number of medical components required to perform the procedure and the increased amount of time required to insert and remove those multiple components.
The guide wire weaving technique is another catheter insertion method known in the art. Using a direct needle stick method for access and insertion, this technique eliminates the need for a sheath. The guide wire is placed into the vein using a normal Seldinger technique. The tissue is dilated with an appropriate size dilator. The catheter is then back loaded and woven over the guide wire. In back loading, the proximal end of the guide wire is inserted into the distal most lumen of the catheter and then the guide wire is threaded out a side hole in the distal most tube and back into the other lumen of the catheter through its distal opening, effectively joining the two catheter tubes together. The catheter is then advanced over the guide wire as a single unit into the target vein.
Although the guide wire weaving method eliminates the need for a sheath, it is a cumbersome process since it requires the physician to manually thread the guide wire through the appropriate holes in the catheter prior to insertion. Another problem with this technique is the likelihood of the catheter shaft accordianing over the guide wire. Attempting to advance a soft-durometer catheter directly over a guide wire may also cause kinking and what is known in the art as accordianing. Friction between the guide wire and the inner wall of the catheter may also create difficulty during the insertion procedure.
In U.S. Pat. No. 5,405,341, Martin discloses a dual-lumen non split tip catheter assembly with a tubular stiffening tube for insertion using a guide wire and the Seldinger technique, a relevant portion of which is illustrated in FIG. 7 herein. Referring to FIG. 7, the unitary catheter assembly includes a first lumen 58 and a second lumen 59 which are positioned side-by-side. The lumens 58, 59 are in a unitary housing over the entire length of the first lumen 58, which is the withdrawal lumen, forming a unitary dual-lumen shaft. A stiffening tube 60 extends through the lumen 58, through the end opening 61 of lumen 58, through an aperture 62 in a distal section of the supply lumen 59 through the distal section of lumen 59 and extends out the end opening 63. This arrangement is adapted to a dual lumen catheter that is not split tip.
It is a major purpose of this invention to provide a split tip blood treatment catheter having the advantage that it is easier for the surgeon to insert into the patient.
A further purpose is to provide such a catheter that does not require a sheath for insertion because it has a design which minimizes tissue damage during placement in a patient.
It is a related purpose to provide the tissue damage minimization advantage without creating the risk of air embolism.
It is a further related purpose of this invention to provide the above objects in a design that minimizes the time and trauma associated with the placement procedure.